The aim of this project is to define the course of the major physiological cations (calcium, sodium, potassium) from surface to interior of the myocardial cell as affected by binding and/or exchange at the glycocalyx, the sarcolemmal bilayer, the mitochondria and the sarcoplasmic reticulum. In addition the cationic binding and exchange characteristics will be related to the contractile properties of the myocardium. The experiments are designed to dissect current models of excitation-contraction coupling so that the various cellular organelles can be realistically placed in a comprehensive model for the role of the ions in control of the heart's function. The studies will utilize various specialized techniques which have been developed or are in the process of development in the PI's laboratory. These techniques are 1) the scintillator-disk flow cell for tissue culture, 2) the "gas dissected" membrane from culture, 3) the arterially-perfused interventricular septum 4) the isolated, single cell from adult rat or rabbit heart (all developed in this laboratory and in routine use), 5) the isolated glycocalyx from culture and the 6) planar-oriented sarcolemma from adult heart (both under advanced development). The long term objective of the PI for the past 20 years has been definition of ionic exchange as it relates to myocardial function. The current proposal is designed to continue to pursue this objective through the use of sophisticated flux and radioisotopic techniques as enumerated above. The pursuit of the long term objective will involve experimentation in 6 areas of study. 1) Control of Ca permeability 2) Sarcolemmal-glycocalyx binding. 3) Transmembranous Ca flux via "carrier" and "channel". 4) Subcellular Ca compartmentalization. 5) Movement and compartmentalization of Na. 6) Identification of specific sites (and molecules) important in control of cation permeability. The techniques have been designed to minimize extrapolation from isolated experimental systems to the intact, functional cardiac cell as these areas of study are pursued. The proposed program is fundamental to the understanding of the basis of myocardial function. This understanding at the cellular level is crucial to further clinical advances.